The present invention relates to an advantageous method of joining areas of dissimilarly shaped members without the need to initially use a spool to begin joinder of the materials. More specifically the invention relates to a quick efficient way to form flute tube having an expanded internal surface area and which is particularly useful when used as a support for a catalyst in a catalytic converter, due to its ability to withstand high temperatures.
It is sometimes necessary to internally fit tubular members with a fluted structure having multiplicity of adjoining, parallel but separated conduits, or flutes, which extend over the full length of a fluted structure to form "fluted tubes" which are useful as flow straighteners and enhanced surface area providers for passing fluids therethrough.
Such a fluted structure has found wide acceptance as a substrate for the strategic elements for the catalytic conversion of noxious components of waste gases, more commonly known as "catalytic converters" which are in wide-spread use in the exhaust systems of internal combustion engines. The efficient, low-cost and high quality production of such a fluted structure is not simple.
Problems arise where the layers of the fluted tubing tend to telescope or extrude axially. Once this occurs, the metal supported catalyst will not remain intact simply under its own winding tension. The use of retaining bars to check the tendency of the fluting to extrude are undesirable due to the added weight as well as the added perturbation of the gas flow.
In one attempt, exemplified by U.S. Pat. No. 4,521,947, issued to Nonnenmann et al on Jun. 11, 1985, and entitled "Method for Manufacturing a Catalytic Reactor Matrix," a fluted tube is constructed by simultaneously winding together a corrugated sheet, a flat sheet, a first pair of soldering bands, and a second pair of soldering bands about a mandrel to form a spirally wound fluted core. The flat and corrugated sheets are soldered to each other to complete the manufacturing process. A serious drawback encountered with this manufacturing process is that it leaves open an undesirable, large center or mandrel core hole. The core hole was necessary to support the sheets during spot welding and because it was difficult or impossible to commence the simultaneous winding of the two sheets without first forming the center hole.
An additional piece, namely a fluted core must then be inserted in a cylindrical envelope, or tube, and secured by a technique such as by soldering the outer portion of the fluted structure to the inside of the tube to form a complete fluted structure. A further shortcoming of the process disclosed in the '947 patent is that the sheets must be soldered to each other, apparently because conventional spot welding techniques cannot be employed since there is neither time nor room for positioning the required electrical spot welding equipment given the relatively large numbers of layers which are formed simultaneously.
In U.S. Pat. No. 4,300,956, issued on Nov. 17, 1981 to Rosenberger et al, entitled "Method of Preparing a Metal Substrate for Use in a Catalytic Converter," a method of co-winding intercalated layers of corrugated and noncorrugated fecralloy sheets is taught. Also taught is the wash coating technique of applying catalysts to the metal substrate. An alumina coat is applied in order to have a surface rough enough to cause a catalyst to adhere. It is also taught that the adhesion of the alumina coat is dependent on the tension to which the metal which underlies the coat is subjected during formation. In a typical roll, the greatest tension is at or adjacent the inner core due to the more highly angled turns, and decreases radially. The method disclosed for fixing the metallic portions of the fluted tubes together is soldering or brazing, which is performed with the additional step of after-heating the formed fluted structure.
U.K. Pat. 1,452,982, entitled "Catalytic Reactor Matrix for Cleaning Internal Combustion Engine Exhaust Gases and a Method of Manufacturing the Same," discloses the exposure of a corrugated and flat sheet of chromium nickel alloy to a coating bath before joining them together into a fluted structure.
The following additional patents represent the current state of the art with respect to the construction and manufacture of flute tubes and include U.S. Pat. Nos. 4,282,186; 4,381,590; 4,400,860; and 4,519,120.